I was able to reproduce on my end with the video provided in the link.
Sometimes the transcoding for a video can be off, and that is what causes the “Upload Failed. Corrupt MP4 file provided” error.
In this case what I usually do is run the video through a video transcoder which outputs a new version of the video with the correct settings.
What I did was run the video through a video transcoder called Handbrake, saved the file, and then uploaded as a background video in Webflow, and all good .